This invention relates to a method of manufacture and in particular relates to a method of manufacturing metal rings of discrete cross-sectional shapes and precise radial diameters.
Metal rings are used throughout industry in a wide variety of applications. Such rings are particularly useful in the construction of parts for gas turbine engines including the construction of vane casings, fan casings, combustor liners, and turbine shrouds. Typically, metal ring structures for gas turbine engines have been constructed from metal ring blanks of rectangular cross-section having a radial diameter and axial width substantially equal to that of the final ring structure and having a cross-sectional thickness equal to or greater than the thickest part of the final ring structure. A lathe is used to cut away excess material from the starting blank in order to achieve a desired cross-sectional contour. Typically in such an operation as much as 90% of the original starting material may have to be removed in order to achieve the desired cross-sectional contour. Accordingly, such prior art machining methods have been found to be both extremely time-consuming and wasteful. This problem is particularly acute in the construction of rings for use in gas turbine engines because of the relatively expensive high temperature metal alloys used, and relatively high cost to machine these tough alloys.
Other processes have been used for manufacturing metal rings such as back extrusion, hot ring rolling and hot or cold rolling a contour on a strip stock and then making a ring therefrom. However, these prior art processes have rarely offered cost reductions over the process of making rectangular sections and machining. Such prior art processes have economic factors which have prevented them from being widely utilized for construction of gas turbine engine parts. Thus, the manufacturing costs for hot rolled ring configurations have been found to be sufficiently high as to make utilization of such processes limited. Further, hot rolling processes have also been found to lack sufficient manageability to be able to hold the close tolerances of size and shape required for gas turbine engine ring structures. Accordingly, in such hot rolling processes it has been necessary to subsequently machine the rolled structure on a lathe in order to obtain the required dimensional tolerances with a resultant undesirable increase in manufacturing time and material waste. Similarly, prior art methods for cold rolling ring structures have been heretofore unable to be utilized successfully for manufacturing metal rings suitable for use in gas turbine engines, without the need for subsequent costly machining.